Patients with cancer who lack effective treatment desperately seek novel interventions that might extend their lives. They do not have time to wait for the US Food and Drug Administration's (FDA’s) regular approval process, which requires that sponsors demonstrate “substantial evidence of clinical benefit (or efficacy) from adequate and well-controlled investigations.”1 Clinicians, for their part, are eager to offer “rational” treatments targeted at the molecular signatures of disease to their sickest patients.